[attach id=262429 size="medium"]An artist’s impression of the Bunostegos, a cow-sized plant-eating reptile that lived more than 250 million years ago.[/attach]

A cow-like reptile that may have been one of nature’s ugliest beasts roamed an isolated desert before the age of the dinosaurs.

The creature’s genus name – bunostegos – means “knobby roof” and gives a clue to its appearance.

About the size of a domestic cow, the plant-eater had bulbous tumour-like growths sprouting from its head and bony armour down its back.

Fossils from bunostegos dating back around 260 million years to the Permian era were found in what is now northern Niger in Africa.

Back in the Permian the earth was dominated by a single continent called Pangea. Bunostegos lived in an isolated desert in the middle of Pangea with a unique fauna.

Cousins of the creature have previously been unearthed which also had bony knobs on their skulls. But those of bunostegos are the largest and most bulbous ever discovered.

Details of the find appear in the Journal of Vertebrate Paleontology.

The discovery suggests that pareiasaurs, the reptile family to which bunostegos belonged, may have evolved in isolation for millions of years.

Climatic conditions may have corralled bunostegos, along with several other reptiles, amphibians and plants, in the centre of the supercontinent.

Geological data also shows that central Pangea was extremely dry, which would have prevented the movement of animals in and out of the region.

Study leader Christian Sidor, from the University of Washington in Seattle, US, said: “Our work supports the theory that central Pangea was climatically isolated, allowing a unique relict fauna to persist into the late Permian.”

Gabe Bever, from the New York Institute of Technology, said: “Our understanding of the Permian and the mass extinction that ended it depends on discovery of more fossils like the beautifully bizarre bunostegos.”